The overall goal of this study is to investigate the "masked hypertension diagnosis", defined by a mean awake ambulatory pressure above a clinically-defined cutpoint and a clinic blood pressure below a clinical cutpoint, and the "masked hypertension effect", defined by the extent to which mean awake ambulatory pressure is higher than clinic blood pressure. Preliminary research suggests that a masked hypertension (MHT) diagnosis is relatively common and is not benign, as it appears to be associated with increased target organ damage as well as an adverse prognosis for cardiovascular (CV) disease. By definition, the masked hypertension diagnosis and the effect are not diagnosed by conventional clinic blood pressure measurement, which raises the possibility that there may be a large number of persons with masked hypertension who would benefit from antihypertensive treatment. While little is currently known about masked hypertension, this proposed multi-faceted study will enable us to determine (1) its prevalence in two large work organizations, (2) how much of MHT is due simply to the instability/unreliability of the blood pressure measures and how much reflects a stable condition, (3) behavioral, social, psychological, and situational factors that predict (and perhaps cause) masked hypertension, and (4) its association with target organ damage. This project will study 1000 randomly selected employees, 500 from each of two large organizations. Participants will have their clinic BP assessed on 3 occasions, wear an ambulatory BP monitor and actigraph (level of physical activity) for 24 hours, and complete ecologically momentary assessments by electronic diary. The employees will also complete a psychosocial questionnaire, and receive a comprehensive non-invasive CV diagnostic evaluation. The questionnaire will assess characteristics of the individual and his/her environment that may contribute to differences between clinic and ambulatory BP. The CV evaluation will assess several early markers of target organ damage, as well as traditional CV risk factors. To the extent that this study increases our understanding of the differences between clinic and ambulatory BP, it will help to explain why the latter is a better indicator of prognosis. We anticipate that it will also contribute to a better understanding of the process by which transient increases in BP can lead, in the long run, to permanent increases in resting BP.